Howstuffworks.com's "How a Car Engine Works"

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How a Car Engine Works
by Marshall Brain

Have you ever opened the hood of your car and wondered what was going on in there? Car engines can look like a big confusing jumble of metal, tubes and wires to the uninitiated. You might want to know what's going on in there simply out of curiosity. After all, you ride in your car every day - wouldn't it be nice to know how it works? Or maybe you are tired of going to the mechanic and having him say things that are totally meaningless to you and then charging you $750 for it. Or perhaps you are buying a new car, and you hear funny words like "3.0 liter V6" and "dual overhead cams" and "tuned port fuel injection". What does all of that mean?

If you have ever wondered about this kind of stuff, then How Stuff Works is glad to help out with this complete guide to how gasoline engines work. Enjoy!

The Beginning
A car is one of the most complicated objects that a person sees during a normal day. Cars have thousands of parts, all of them functioning reliably together day in and day out. However, the basic principles behind all car engines are very simple and once you understand them many different things about cars make a lot more sense.

So let's start at the very beginning: Why do you have a car? Answer: To move your body and your stuff from one place to another. That is what a car does. If you could step into a phone booth, dial a number and somehow instantly transmit your body to another place (like they do in Star Trek with the transporter room) would you have a car? No way. That's why no one on Star Trek has a car. [Of course it forces you to ask why Captain Kirk needs a ship - why didn't everyone just stay on planet Earth and beam themselves to all these different places instantaneously rather than messing with the Starship Enterprise? Maybe transporter beams can only travel so far...]

So you have a car to get around until someone invents the transporter room. The next question is: Why is nearly every car, motorcycle, moped and even lawn mower powered by gasoline? Because gasoline has an extremely high energy density, because it is cheap (relative to the alternatives) and because it is easy and relatively safe to move around. For comparison, it takes about 1,000 pounds of lead-acid batteries to store the same amount of energy that one gallon (7 pounds) of gas contains. It will take you several hours to recharge the batteries but it takes about 15 seconds to pump one gallon of gas. That is why you do not see very many electric cars right now - Gas is a lot easier.

The purpose of a gasoline car engine, therefore, is to convert gasoline into motion so that the car can move. Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine. Therefore, a car engine is generally referred to as an internal combustion engine. Two things to note:

There is such a thing as an external combustion engine. Steam engines in old-fashioned trains and steam boats are the best examples of external combustion engines. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. It turns out internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus internal combustion engines are a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

There are also different kinds of internal combustion engines. The gas turbine engine is another form of internal combustion engine. Gas turbine engines have interesting advantages and disadvantages, but their main disadvantage right now is an extremely high manufacturing cost (meaning they cost more than piston engines used in cars today). Click here for more information on gas turbines.

Almost all cars today use reciprocating internal combustion engines because these engines are relatively efficient (compared to external combustion engines), relatively inexpensive (compared to gas turbines) and relatively easy to refuel (compared to an electric car). These advantages beat any other existing technology for moving a car around.

To understand a car engine you have to start by understanding how internal combustion in a piston engine works.

Go to the next article about Engines or pick from the table of contents:

The Beginning You are here
Internal Combustion
Parts of an Engine
What Can Grow Wrong
Engine Subsystems
How to Help an Engine Produce More Power
Questions and Answers
List of Books and Links

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